Combustion chambers of gas turbine engines



April 26, 1955 s. ALLEN ETAL 2,706,889

COMBUSTION CHAMBERS 0F GAS TURBINE ENGINES Filed July 19, 1950 2 Sheets-Sheet 1 2s 22 2o 36 23 N Z4 26 I I 7 I; I, I 1 1| f 4| 1 r K I 3 I I! F 1 Q 33 I :9 :z 2! 3B INVENTOR 5IONV .4416 f y M 4. 379x63 April 26, 1955 s, LLEN 'ETAL Y 2,706,889

COMBUSTION CHAMBERS 0F GAS TURBINE ENGINES Filed July 19. 1950 2 Sheets-Sheet 2 INVENTORS WWW United States Patent COMBUSTION CHAMBERS OF GAS TURBINE ENGINES Sidney Allen and Morris A. Stokes, Coventry, England, assignors to Armstrong Siddeley Motors Limited, Coventry, England Application July 19, 1950, Serial No. 174,736 Claims priority, application Great Britain Augist 1S, 1949 3 Claims. (Cl. 6039.71)

This invention relates to a liquid fuel combustion chamber, particularly for a gas turbine engine, of the kind incorporating a plurality of J-like pipes which deliver a mixture of fuel and primary air to the interior of a flame chamber in which the pipes are placed and to which is added secondary air substantially to complete combustion in the flame chamber and preheat the pipes to assist in vaporizing the fuel in the mixture of fuel and primary air.

It is found in practice that hot spots are liable to occur in these pipes due to the fact that a complete scouring of the whole of the inner walls by the mixture of fuel and primary air does not always take place. This is particularly so at the inner walls of the curves of pipes with semi-circular bends, due, possibly, to centrifugal forces acting on the mixture in the bends tending to scour the outside walls very thoroughly and to leave the inside walls insufficiently scoured. This may shorten the effective life of the pipes and impair the correct vaporizing of the fuel owing to the inefficient transfer of heat from the walls to the fuel particles at such zones.

The main object of the present invention is to avoid the formation of such hot spots, thereby improving the vaporizing function of the pipes and prolonging their lives.

To this end the invention broadly consists in the provision of means adapted to create local turbulence to the flow at a point in such a pipe at which a hot spot is likely to occur, whereby particles of fuel in the mixture are thrown into more intimate contact with the inner wall of the pipe. In this way a better heat transference is provided by the scouring action of the fuel particles.

Such means may be solid or hollow projections fixed to the walls of the pipes and extending across the flow path. In their simplest form the projections may be of cylindrical shape, but they may have other shapes or forms to promote a greater or less degree of local turbulence as desired. They may be arranged to be at right angles to the flow, or otherwise, and, if hollow projections are used, they may be disposed so that some of the burning mixture in the flame chamber may flow through them and thus improve vaporization.

According to a further feature of the invention, the bends in the pipes, instead of being substantially semicircular, are each formed of two mitred joints interconnected by a straight portion. By introducing mitred joints, sufiicient turbulence is set up in the mixture in the bends to ensure a thorough scouring of the whole of the wall of the bend.

With a J-like pipe having a curved bend, the minimum distance of the outlet end from the main portion of the pipe is limited by the permissible minimum radius of the bend; but with a J-like pipe having two mitred joints as aforesaid, the interconnecting straight portion can, in general, be reduced in length so as to permit of the outlet end of the pipe being nearer the main portion when desired than in the ease of a pipe having a curved bend.

In the accompanying drawings:

Figure 1 is a fragmentary sectional elevation of one form of liquid fuel combustion chamber according to the invention, the section being taken mainly on the line 11 of Figure 2;

Figure 2 is an axial elevation thereof taken mainly on the line 2-2 of Figure 1;

Figure 3 is an elevation, to a larger scale, of one of the J-like pipes of Figures 1 and 2;

" ice pipe adapted according to the invention;

Figure 5 is a fragmentary section of part of the pipe of Figures 1 and 2, and Figure 6 a corresponding section taken at right angles thereto;

Figures 7, 9 and 11 are fragmentary sections corresponding to that of Figure 5 but showing alternative arrangements; and

Figures 8, l0 and 12 are fragmentary sections taken at right angles respectively to Figures 7, 9 and 11.

The combustion chamber shown includes an outer casing 20 along which air compressed by the compressor of a gas turbine engine (not shown) travels from left to right (in Figure l). The flame chamber 21 is constituted by three axially-spaced tubes 22, 23 and 24, the middle one 23 being disposed so that its ends axially overlap the adjacent ends of the two end tubes 22 and 24 with radial clearance as shown. The flame chamber 21 is held spaced radially from the outer casing, as by means of struts 25, 26, to provide an annular passage 27 along which travels diluent air Which serves for cooling the flame chamber externally and which mingles with the products of combustion issuing from the flame chamber to reduce their temperature to a suitable value. Some of this diluent air enters the annular openings 28, 28 to cool the tubes 23 and 24 internally.

In the present instance, there are four J-like pipes 30, the main portions thereof being supported at their inlet ends 31 in a bafile plate 32 closing the inlet end of the flame chamber 21. Some of the air passing within the outer casing 20 enters the inlet ends 31 of these pipes and serves as primary air. 33 represents a fuel supply means whereby liquid fuel will be sprayed into the inlet ends 31 of the pipes to mix with the primary air therein. The fuel and primary air issue from the outlet ends 34 of the pipes as a combustible mixture, and suflicient secondaryair to ensure combustion substantially within the flame chamber 21 is supplied to the latter through slits 35 in tubular nozzles 36 mounted in the baifie plate. The nozzles 36 are, it will be observed, disposed angularly clear of the outlet ends 34 of the pipes. The burning mixture within the flame chamber serves for externally heating the pipes anl thus for vaporizing the fuel therein admixed with the primary air, in consequence of which very satisfactory combustion is ensured.

In Figures 1, 2 and 3 the bend of each J-like pipe 30, instead of being substantially semi-circular, is formed of two mitred joints 37, 38 interconnected by a straight portion 39. By means of these sharp rightangled bends sufficient turbulence is set up in the mixture of fuel and primary air at these bends to ensure a thorough scouring of the whole of the inner Wall of the bend.

In addition, the drawings show projections 41 extending across and fixed to the walls of the main portions of the pipes and serving to introduce turbulence whereby to increase the scouring of the inner walls of these portions of the pipes, thus both to cool these portions of the pipes and to increase the vaporization of the fuel in the mixture of fuel and primary air.

As shown most clearly by Figures 5 and 6, these projections 41 may be cylindrical ones. Alternatively, as shown by Figures 7 to 12, they may take other shapes, Figures 7 and 8 showing a projection 41a of triangular section, Figures 9 and 10 an inclined projection 41b of elliptical section and with open ends so that the flaming mixture can pass through it, and Figures 11 and 12 a projection in the form of an inclined slat 410.

As stated, Figure 4 shows an alternative and known form of J-like pipe 30a to which projections 41, 41a, 41b or 41c, as previously described, are applied not only in the main portions of the pipe but also in the bends, in order to introduce turbulence at any point in a pipe at which a hot spot is likely to occur, whereby particles of fuel in the mixture are thrown into more intimate contact with the inner wall of the pipe.

What we claim as our invention and desire to secure by Letters Patent of the United States is:

l. A J-like pipe structure through which is to be passed liquid fuel in a high-velocity stream of air for vaporization in the pipe by the heat generated outside the pipe by the combustion of vapour after emergence from the pipe,

the inertia of the vapour urging it, due to a change in direction of the pipe bore, to leave unscoured a portion of said bore with resultant over-heating of said portion, characterised by the provision of a combustion chamber surrounding the pipe and in which the vapour is combusted after emergence from the pipe, said pipe having a straight main portion at the inlet end and a parallel turned-back portion at the outlet end, said inlet and outlet portions interconnected, with mitred joints, by an intermediate straight portion, the convex edges Within the pipe 0t said mitred joints creating turbulence in the flow whereby to constrain it, in opposition to said inertia effect, to scour the first said portion.

2. A liquid fuel combustion chamber comprising a flame chamber, and a plurality of J-like pipes each having an inlet portion and an outlet portion disposed within said flame chamber in spaced substantially parallel relation to one another, one end of each inlet portion adapted to be in communication with a source of air and fuel and one end of each outlet portion discharging into said flame chamber, a substantially straight pipe portion joining the other ends of each inlet and outlet portion and being disposed at substantially right angles to the inlet and outlet portions so as to change the direction of flow of the air and fuel mixture through the pipes.

3. For use with a combustion chamber in which a vapour is adapted to be ignited, a J-like pipe adapted to be positioned within the combustion chamber and having an inlet portion and an outlet portion disposed in substantially parallel spaced apart relation to one another, said inlet portion having an inlet opening at one end for receiving a supply of air and fuel, said outlet portion having a discharge opening at one end adapted to discharge the air and fuel mixture into the combustion chamber, said pipe also having a substantially straight potrion connecting the other ends of the inlet and outlet portions.

References Cited in the file of this patent UNITED STATES PATENTS 89,426 Norton Apr. 27, 1869 461,058 Tocin Oct. 13, 1891 1,315,853 Nordling et al. Sept. 9, 1919 1,399,236 Yamashita Dec. 6, 1921 2,016,720 Krause Oct. 8, 1935 2,081,612 Woodson May 25, 1937 2,216,046 Peck Sept. 24, 1940 2,411,663 McCollurn Nov. 26, 1946 2,483,737 Parrish Oct. 4, 1949 2,522,081 Allen Sept. 12, 1950 2,541,900 Williams Feb. 13, 195! FOREIGN PATENTS 603,485 Great Britain June 16, 1948 

3. FOR USE WITH A COMBUSTION CHAMBER IN WHICH A VAPOUR IS ADAPTED TO BE IGNITED A J-LIKE PIPE ADAPTED TO BE POSITIONED WITHIN THE COMBUSTION CHAMBER AND HAVING AN INLET PORTION AND AN OUTLET PORTION DISPOSED IN SUBSTANTIALLY PARALLEL SPACED APART RELATION TO ONE ANOTHER, SAID INLET PORTION HAVING AN INLET OPEINING AT ONE END FOR RECEIVING A SUPPLY OF AIR AND FUEL, SAID OUTLET PORTION HAVING A DISCHARGE OPENING AT ONE END ADAPTED TO DISCHARGE THE AIR AND FUEL MIXTURE INTO THE COMBUSTION CHAMBER, SAID PIPE ALSO HAVING A SUBSTANTIALLY STRAIGHT PORTION CONNECTION THE OTHER ENDS OF THE INLET AND OUTLET PORTIONS. 